This invention relates to wireless communications, and more particularly, to wireless communications in networks such as cellular networks.
A cellular network is a wireless network that includes multiple cells and base stations. Base stations are towers for mounting antennas, transceivers, and other wireless communications equipment. Each cell is served by one or more respective base stations. Base stations are sometimes referred to as cell sites, cell towers, base transceiver stations (BTS), etc. In a typical cellular network, base stations may be located close to one another (e.g., ¼-½ mile apart) or far away from one another (e.g., 1-2 miles apart). Base station spacing generally depends on the number of active users served by each base station and considerations such as cell site topography.
Cellular base stations provide radio coverage for user equipment (UE) such as portable user devices. An example of a portable user device is a mobile phone that is used to make telephone calls. The user device may communicate wirelessly with a neighboring base station that is providing radio coverage. Base stations may collectively provide radio coverage that covers a wide geographic region. The radio coverage of each cell may be approximately circular. The radio coverage of each cell typically overlaps with the radio coverage at least one other cell to provide a continuous region of radio coverage for the cellular network. The amount of overlap between adjoining cells should generally not be too large to minimize waste and to minimize potential interference among the cells.
A cellular network implemented using a wireless telephony protocol such as the Global System for Mobile communications (GSM) protocol or a code division multiple access (CDMA) protocol. Regardless of what technology is used, user devices should be able to move from cell to cell (e.g., the wireless technology should support a handover mechanism) without losing wireless connectivity.
User devices such as mobile phones are typically designed to operate over a range of possible transmit powers. Wireless communications systems use transmit power control (TPC) commands to control the transmit powers of user devices in the system. Consider a first scenario in which a user device is transmitting at maximum power levels to a base station. If there are other devices that are also communicating with the base station, the signal transmitted by the user device may be too strong and may interfere with the signals transmitted by the other devices. If the full power of the devices is not required for satisfactory communications, the base station may send a TPC command that instructs the user device to transmit at a lower power level. By reducing transmit powers whenever possible, interference can be reduced and the number of simultaneous users can be maximized. Reduction in transmit power may be common in urban regions that have dense populations of active user devices and short distances between cell towers.
In contrast, consider a second scenario in which a user device is transmitting at a low power. If the transmit power is too weak, the base station may not be able to properly receive the transmitted signal from the user device. In this scenario, the base station may send a TPC command that tells the user device to transmit at a higher power level. Operation at higher powers may be common in suburban regions that have sparser populations of active user devices relative to urban regions. Because not as many user devices are simultaneously communicating with a given base station and because cell signals must travel greater distances, user devices may transmit at higher powers.
Because of the differences in topology and cell usage patterns in different geographic locations, cellular telephones tend to operate at different powers in different environments. For example, cellular telephones in urban environments may tend to operate at lower transmit powers than cellular telephones in suburban areas. Each different type of operating environment may, in general, be characterized by its own unique set of cellular telephone transmit power statistics.
In conventional networks, cellular telephones are provided with a single set of transmitter settings. These settings dictate how the cellular telephone transmits cellular signals under different conditions. For example, the transmitter settings may dictate that low transmit powers should be produced by activating a single radio-frequency power amplifier gain stage in the cellular telephone, whereas high transmit powers should be produced by activating two radio-frequency power amplifier gain stages.
Although use of a generic set of transmitter settings for all cellular telephones in a cellular telephone network may be straightforward to administer, inefficiencies and performance issues may arise during operation. In particular, the generic transmitter settings might result in high call quality in suburban environments or other environments where transmit powers tend to be high, but may result in suboptimal call quality in urban environments. As another example, the generic transmitter settings might result in excellent transmitter power efficiency performance in urban environments, but might exhibit lower than desired transmitter power efficiency performance in suburban environments.
Because call quality and power consumption must be acceptable for all users, the generic transmitter settings that networks use represent a compromise. Settings are not optimized for either urban or suburban environment, but rather are selected so that adequate performance is obtained on average.
Although use of generic transmitter settings is generally satisfactory, recent advances in cellular telephones are placing increasing demands on cellular networks and cellular telephone manufacturers. Increased cellular telephone usage is giving rise to a greater potential for interference between devices. Battery life is also of growing importance, because users are using their cellular telephones to browse the Internet and handle other power-intensive tasks.
It would therefore be desirable to be able to provide ways in which to optimize the performance of wireless networks and wireless electronic devices such as cellular telephones.